Arrays of identical or substantially structurally similar switched capacitor elements can be electrically combined into banks (e.g., through interconnects) to provide a given amount of collective capacitance. In previous implementations of such arrays, sub-banks have been grouped and driven with single control lines to minimize the number of driving circuits required. This configuration can use a mixture of linear and binary control sequences. As binary boundaries are reached, some sub-banks are turned on and others off. This may create a transient where the total bank capacitance varies outside of the range between the starting and finishing states. For cold-switching, this is not an issue. However, for hot switching where the circuit is in operation during the switching event, this may cause an undesired response of the circuit using the capacitor during the transient. Additionally, the fixed grouping of the elements leads to high switching rates and specific distributions of element switching rates that depend heavily on the application.
For example, as shown in FIG. 1, a plurality of switched capacitor elements 10 are arranged in an array 100. In particular, as shown in FIG. 1, array 100 can be an 8×8 array comprising 64 of the elements 10. For instance, elements 10 can each have a 250 fF capacitance change for a total tuning range of 16 pF. Elements 10 can be grouped into binary element groups to minimize the number of control lines needed to select any of the plurality of the elements 10. In the 8×8 array shown in FIG. 1, for example, the 64 elements 10 can be grouped into six control bits. In this arrangement, there exists a single bit 10a that is not easily combined into the binary scheme. In conventional control arrangements, this single bit could be configured as a comparatively smaller capacitance bit (e.g. 125 fF compared to 250 fF) to add resolution and maintain the binary control for a total of 7 bits as shown in FIG. 2.
In one particular case in which the total capacitance of the array is switched from 7.75 pF (e.g., binary control word of 011111) to 8.00 pF (e.g., binary control word of 100000), this single bit change in total capacitance results in nearly all of the bits changing state as shown in FIG. 3. This nearly entire switching can contribute to lower product life and, depending on which transition is faster, might result in temporarily having nearly the full array capacitance or nearly none of the array capacitance at some point during the transition. For devices where opening starts earlier than closing, for example, the tuning capacitance would drop briefly to near zero. This drop would impact circuit performance during the transient so this could be a critical shortcoming for hot switching applications. Also, when wearout is a lifetime limiter, this approach causes wear on all elements.
Accordingly, it would be desirable for an array control system and method to effectively control the operation of an array of individually switchable elements without capacitance excursions during tuning and without array lifetime limitations.